Unitary composite steering wheel and air bag cover assembly and method of making same

ABSTRACT

A unitary composite steering wheel and air bag cover assembly includes a one-piece plastic body having an air bag cover portion, a one-piece rear rim portion molded from a plastic material compatible with the plastic of the body and a one-piece skeletal frame structure including a rim portion encapsulated therebetween. The plastic may be either a thermoplastic or a thermosetting plastic. In one embodiment, circular front contact surfaces of the rear rim portion bond with circular back contact surfaces of a front rim portion of the body by diffusion between the contact surfaces thereof with the frame structure therebetween. The resulting assembly is hardened so that a molecular concentration gradient is formed at an interface between the plastics to bond the plastics by diffusion. In another embodiment, the rear rim portion and the body are molded from the same plastic material in a single mold cavity with the rim portion of the frame structure encapsulated therebetween and an air bag aperture of the frame structure covered by and aligned with the air bag cover portion at its predetermined tear seam design.

TECHNICAL FIELD

This invention relates to steering wheels and air bag cover assembliesand methods of making same, and, in particular, to plastic steeringwheels and air bag cover assemblies and methods of making same.

BACKGROUND ART

Supplemental occupant restraint systems for motor vehicles (i.e., airbags) typically require covers which allow an air bag to exit the airbag cover when deployed. One type of air bag cover includes a frontpanel which has a predetermined tear seam design formed therein to allowthe air bag to exit the air bag cover when deployed.

Not only must the air bag cover perform the utilitarian function ofbreaking apart along its predetermined tear seam design, but it shouldalso match the vehicle interior decor and trim materials such as theinstrument panel, seats, door panels, steering wheel and posts.

Also, not only must the air bag cover allow the air bag to exit the airbag cover when deployed, but also the air bag cover must stay togetherto the extent that it does not break apart so as to presentprojectile(s) which may injure an occupant of the motor vehicle. U.S.patent to Goetz et al., U.S. Pat. No. 3,984,126 discloses a unitarysteering wheel and air bag cover assembly made from plastic.

The U.S. patent to Onishi et al., U.S. Pat. No. 5,358,273 also disclosesa unitary steering wheel and air bag cover assembly.

The U.S. patent to Cuevas, U.S. Pat. No. 5,277,442 discloses an air bagsystem including a vehicle steering wheel having a structural framewhich includes a integral retainer. The system also includes a coverwhich, together with the retainer forms a container.

The U.S. patent to Chen et al., U.S. Pat. No. 5,228,362 discloses avehicle steering wheel having an armature which defines a structuralcircular steering wheel.

The U.S. patents to Humphreys et al.,U.S. Pat. No. 5,348,340, Breed etal., U.S. Pat. No. 5,419,585, and Proos et al., U.S. Pat. No. 5,335,935all disclose conventional steering wheel assemblies having an air bagsubassembly.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a unitary compositesteering wheel and air bag cover assembly including a one-piece plasticbody injection molded at a first injection station and a one-piece rearrim portion injection molded at a second injection station from aplastic material compatible with the plastic of the body so that acircular front contact surface of the rear rim portion bonds with acircular back contact surface of a front rim portion of the body bydiffusion between the contact surfaces thereof.

Another object of the present invention is to provide a unitarycomposite steering wheel and air bag cover assembly wherein an air bagcover portion perfectly matches a rim of the assembly in color and otherphysical characteristics.

Yet still another object of the present invention is to provide a methodfor making a unitary composite steering wheel and air bag cover assemblyfor an inflatable air bag system.

In carrying out the above objects and other objects of the presentinvention, a unitary composite steering wheel and air bag cover assemblyis provided. The assembly cover includes a one-piece, plastic bodyinjection molded at a first injection station and including a front rimportion and an air bag cover portion with a predetermined tear seamdesign formed therein. The front rim portion includes a circular backcontact surface. The air bag cover portion is adapted to overlie aninflatable air bag system. The assembly also includes a one-piece rearrim portion injection molded at a second injection station from aplastic material compatible with the plastic of the body so that acircular front contact surface of the rear rim portion bonds with theback contact surface of the front rim portion by diffusion between thecontact surfaces thereof at one of the first and second injectionstation to prevent the body from separating from the rear rim portionduring use of the assembly. Finally, the assembly includes a one-pieceskeletal frame structure including a circular rim portion totallyenclosed within the bonded front and rear rim portions. The framestructure has an aperture aligned with the air bag cover portion toallow an air bag of the air bag system to exit the air bag cover portionwhen deployed.

Also in carrying out the above objects and other objects of the presentinvention, a method is provided for making a unitary composite steeringwheel and air bag cover assembly for an inflatable air bag system. Themethod includes the steps of injecting a first molten plastic at a firstinjection station having a shape defining a first part including a rimportion, hardening the resulting first part and moving the hardenedfirst part and a skeletal frame structure into a second injectionstation having a shape defining the entire assembly. The method alsoincludes the steps of injecting a second molten plastic at the secondinjection station at a temperature and pressure sufficient to melt asurface layer of the rim portion of the first part, and hardening theresulting assembly so that a molecular concentration gradient is formedat an interface between the first and second plastics to bond the firstand second plastics by diffusion with the skeletal structuretherebetween. Finally, the method includes the step of removing thecompleted assembly from the second injection station.

Still further in carrying out the above objects and other objects of thepresent invention, a unitary composite steering wheel and air bag coverassembly is provided. The assembly includes a one-piece, plastic bodyinjection molded in a mold. The body includes a front rim portion and anair bag cover portion with a predetermined tear seam design formedtherein. The air bag cover portion is adapted to overlie an inflatableair bag system. The assembly also includes a one-piece rear rim portioninjection molded in the mold from the same plastic material of the bodyso that the rear rim portion bonds with the front rim portion in themold to prevent the body from separating from the rear rim portionduring use of the assembly. Finally, the assembly includes a one-pieceskeletal frame structure including a circular rim portion totallyenclosed within the bonded front and rear rim portions. The structurehas an aperture aligned with the air bag cover portion to allow an airbag of the air bag system to exit the air bag cover portion whendeployed.

Yet further in carrying out the above objects and other objects of thepresent invention, a method is provided for making a unitary compositesteering wheel and air bag cover assembly for an inflatable air bagsystem. The method includes the steps of inserting a skeletal framestructure having an air bag aperture surrounded by a rim portion into amold cavity of a mold having a shape defining the entire assembly, andinjecting a molten plastic into the mold cavity of the mold to cover theentire top surface of the structure, the air bag aperture and the entirerim portion of the structure. The method also includes the step ofhardening the resulting assembly. Finally, the method includes the stepof removing the completed assembly from the mold.

In each of the above methods and assemblies, the plastic may be either athermoplastic or a thermo-setting plastic.

The above objects and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the best mode for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a unitary composite assemblysteering wheel and air bag cover assembly constructed in accordance withthe present invention;

FIG. 2 is an exploded view of the assembly together with other partsincluding mounting parts of an air bag system adapted to be mounted atan end of a steering wheel post;

FIG. 3 is a schematic view of a pair of conventional injection moldingsystems which may be utilized to make the assembly of the presentinvention;

FIG. 4 is a block diagram flow chart illustrating the various methodsteps taken to practice a first embodiment of the method of the presentinvention in order to make the assembly; and

FIG. 5 is a block diagram flow chart of a second embodiment of themethod.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawing figures, there is illustrated in FIG. 1 aperspective view showing an embodiment of a unitary composite steeringwheel and air bag cover assembly, generally indicated at 10, constructedin accordance with the present invention. The assembly 10 preferably isinstalled over an inflatable air bag system, a support structure ofwhich is generally shown at 12 in FIG. 2, mounted at the end of asteering wheel post (not shown). The occupant restraint air bag systemis typically mounted at the interior end of the steering wheel postadjacent the assembly 10 so that the air bag may deploy between thevehicle driver and the steering wheel post to prevent injury during anaccident or other period of sudden deceleration.

Referring specifically now to FIG. 2, there is illustrated in detail anembodiment of the assembly 10 constructed in accordance with the presentinvention. The assembly 10 includes a one-piece injection molded plasticbody, generally indicated at 14, which is preferably injection molded ina first mold at a first injection station (FIG. 3) and has apredetermined tear seam design as indicated at 16 formed in an air bagcover portion 18. The air bag cover portion 18 is adapted to overlie aninflatable air bag system. The plastic body 14 also includes a front rimportion 20 having circular back contact surfaces (not shown) but whichare substantially identical to circular front contact surfaces 22 of aone-piece rear rim portion, generally indicated at 24, of the assembly10.

The assembly 10 also includes a one-piece skeletal frame structure,generally indicated at 26. The frame structure 26 is preferably madeinto a wire frame, a casting or a stamping from metal, such as steel,and includes a circular rim portion 28. The frame structure 26 alsoincludes a central support portion 29 having a plurality of apertures30, 32 and 34 formed therethrough. The aperture 30 is aligned with thecover portion 18. An air bag of the air bag system exits through theaperture 30 and through the cover portion 18 when deployed.

The support portion 29 preferably has a plurality of threaded holes 36formed about the aperture 30 to receive and retain a like plurality ofthreaded fasteners 38. The fasteners 38 secure a steel inflator assemblycollar 40 of the support structure 12 to the frame structure 26 at holes42.

As noted above, the assembly 10 also includes the one-piece rear rimportion 24 injection molded in a second mold at a second injectionstation (also FIG. 3) from a plastic material compatible with theplastic of the body 14 so that the circular back contact surfaces of thefront rim portion 20 bond with the front contact surfaces 22 of the rearrim portion 24 by diffusion between the surfaces thereof in the secondmold to prevent the body 14 from separating from the rear rim portion 24during use of the assembly 10.

Preferably, the plastic of the body 14 is a thermoplastic such as TPO,TPU, DYM, (a trademark of the DuPont Company for certain types ofthermoplastics); santoprene, etc., whereas the plastic material of therear rim portion 24 is a compatible plastic. Alternatively, the plasticsmay be a thermosetting or RIM (reaction injection molding); plastic orother type of plastic such as RIM urethane.

Typically, if the plastic is a thermoplastic, the durometer of the body14 will be in the range of about 37 Shore D to 52 Shore D, while theflexural modulus will be in the range of about 30,000 to 70,000 psi. Ifa RIM plastic is used, the modulus could be lower.

The support structure 12 also includes a plastic trim plate 44, a metalmounting rim 46 with attachment flanges 48 and a steering column cowl 50having a close-out seal 52.

Referring now to FIG. 3, there is illustrated a first conventionalinjection molding system or injection station, generally indicated at210, and a second conventional injection molding system or injectionstation, generally indicated at 210', for collectively making theunitary composite steering wheel and air bag cover assembly 10 of thepresent invention.

However, it is to be understood that other methods and systems may beutilized to make a unitary composite steering wheel and air bag coverassembly of the prevent invention. For example, a rotating or indexingplaten or table may be used at a single injection or RIM molding systemor injection station.

A further alternative is to place the skeletal frame structure 26 withina single mold cavity which may have pins on which the frame structure 26can be elevated. Then, a molten resin is injected into the cavity allaround the structure 26 so that the assembly 10 is formed. Then theholes in the assembly 10 caused by the pins may be filled or, if smallenough, left alone. Alternatively, the back surface of the structure 26rests on a surface of a mold half so that the back surface of thestructure 26 does not contact the plastic except for the entire rimportion 28 thereof.

Only the first injection station 210 will be specifically described andnot the second injection station 210' or any other system or station.However, it is to be understood that parts of the second injectionstation 210' which have the same or similar function to the parts of thefirst injection station 210 have the same reference numeral except witha prime designation.

Briefly, the injection molding station 210 includes an injection moldingmachine, generally indicated at 212, having a nozzle, generallyindicated at 214, for injecting predetermined amounts or shots of moltenresin. The injection molding machine 212 includes a hydraulic screw ram216 which is disposed in a bore 218 formed in a barrel 220 of theinjection molding machine 212. The ram 216 plasticizes and advancesresin towards the nozzle 214. Upon complete plasticization of the resin,the screw ram 216 is hydraulically advanced towards threaded portions222 of the barrel 220 to inject molten plastic through the nozzle 214,as is well known in the art.

The station 210 also includes a mold or mold body generally indicated at228. As illustrated in FIG. 3, the mold 228 comprises a two-plate moldbody. One of the plates includes a locating ring 230 for locating theinjection end of the nozzle 214. The locating ring 230 is mounted on aclamp plate 232 which, in turn, is fixably connected to a cavityretainer plate or cavity plate 234. A sprue bushing 236 is disposedwithin the locating ring 230 and is supported by the clamp plate 232.Leader pins 238 on the cavity plate 234 provide the male half of themale-female connection of the first plate with the second plate of thetwo-plate mold 228. In particular, the second plate includes leader pinbushings (not shown) which slidably receive and retain the leader pinstherein in the closed position of the mold 228. The leader pin bushingsare retained within a core retainer plate 242. The core retainer plate242 is fixably connected to a support plate 244 which, in turn, isconnected to an injector retainer plate 246. The injector retainer plate246 is connected to an injector plate 248 which, in turn, is supportedby support pillars 250. Support plate 244 is also fixably connected tothe ends of a U-shaped ejector housing 252 to which the support pillars250 are also connected. The plate 246 supports a plurality of returnpins 254 and ejector pins 256 which extend toward the plate 234 andthrough the plates 242 and 244. The ejector pins 256 are provided forejecting particular injection molded part(s) from the mold 228.

Opposing surfaces of male and female mold parts 258 and 260 respectivelydefine a mold cavity 262. The mold part 258 is supported on the plate242 and the mold part 260 is supported on the cavity retainer plate 234.

As illustrated in FIG. 3, there is schematically illustrated how theone-piece thermoplastic body 14 is first molded at the first injectionstation 210 then placed in the mold cavity 262' with the one-pieceskeletal frame structure (not shown in FIG. 3). Thereafter, a one-piecerear rim portion 24 is molded in the second plastic injection station210' thereover the frame structure at its rim portion to form thecompleted unitary composite steering wheel and air bag cover assembly,generally indicated at 10, wherein the one-piece rear rim portion 24overlies the body 14.

Referring now to FIG. 4, there is illustrated the various process stepsof the method of the present invention with further reference to FIG. 3.

At block 400, initially the first molten plastic is injected into thefirst mold cavity of the first injection station through its injectionnozzle 214.

At block 402, the resulting part 14, if formed from a thermoplastic, iscooled to a temperature beneath the softening point of the plastic. Ifthe plastic is a thermosetting plastic, the plastic is heated until theplastic is hardened.

At block 404, the part 14 is moved into a second injection stationtogether with the skeletal frame structure 26. In an indexing system,the part is indexed from the first injection station into the secondinjection station.

At block 406, the second molten plastic is injected at the secondinjection station through its injection nozzle 214' at a temperature andpressure sufficient to melt a surface layer of a rim portion of the part14.

At block 408, the resulting steering wheel and air bag cover assembly 10is cooled to a temperature beneath the softening point of both plasticswhen the plastics are thermoplastics. When the plastics arethermosetting plastics, the plastics are heated.

Finally, at block 410, the completed steering wheel and air bag coverassembly 10 is removed from the second injection station.

Referring now to FIG. 5, there is disclosed in block diagram flow chartform an embodiment of a method for forming another unitary compositesteering wheel and air bag cover assembly of the present invention. Theunitary composite steering wheel air bag cover assembly of the secondembodiment is identical to the assembly 10 of the first embodimentexcept the front rim portion does not include a circular back contactsurface and the rear rim portion does not include a circular frontcontact surface since the front and rear portions bond together in thesame mold cavity and are made from the same plastic material.

With specific reference to FIG. 5, at block 500, a mold is opened andthe skeletal frame structure 26 having the air bag aperture 30 and therim portion 28 is inserted into a mold cavity. The mold cavity has ashape defining the entire assembly. The structure 26 may be supported onpins within the cavity or may rest on a mold half as long as theexterior outer surface of the rim portion 28 can be encapsulated withmolten resin within the mold cavity.

At block 502, the molten resin is injected into the mold through itsinjection aperture to cover the entire top surface of the structure 26,the air bag aperture 30, and the entire rim portion 28 of the structure26.

At block 504, the resulting steering wheel and air bag cover assembly 10is cooled to a temperature beneath the softening point of the resin whenthe plastic resin is a thermoplastic. When the plastic is athermosetting plastic, the plastic is hardened by heating.

Finally, at block 506, the mold is open and the completed steering wheeland air bag cover assembly 10 is removed from the mold.

In this way, the assembly 10 is formed from the structure 26 and amolten plastic which forms a one-piece body 14 including an integralfront rim portion 20, an integral air bag cover portion 18 with apredetermined tear seam design 16 formed therein, and an integrallyformed one-piece rear rim portion 24 in a single mold cavity. The airbag cover portion 18 with the predetermined tear seam design 16 and thealigned aperture 30 allow an air bag to exit the cover portion 18 whendeployed.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative designs and embodiments for practicing theinvention as defined by the following claims.

What is claimed is:
 1. A unitary composite steering wheel and air bagcover assembly comprising:a one-piece, plastic body including a frontrim portion and an air bag cover portion with a predetermined tear seamdesign formed therein, the front rim portion including circular innerand outer back contact surfaces and the air bag cover portion beingadapted to overlie an inflatable air bag system; a one-piece rear rimportion including circular inner and outer front contact surfaces madefrom a plastic material compatible with the plastic of the body so thatthe circular inner and outer front contact surfaces of the rear rimportion bond with the circular inner and outer back contact surfaces ofthe front rim portion, respectively by diffusion between the contactsurfaces thereof to prevent the body from separating from the rear rimportion during use of the assembly; and a one-piece skeletal framestructure including a circular rim portion totally enclosed within thebonded front and rear rim portions between the bonded inner and outerfront and back contact surfaces and having an aperture aligned with theair bag cover portion to allow an air bag of the air bag system to exitthe air bag cover portion when deployed.
 2. The assembly as claimed inclaim 1 wherein the frame structure includes a central support portionhaving the aperture and adapted to be connected to the air bag systemabout the aperture.
 3. The assembly of claim 1 wherein the plastic ofthe body is a thermoplastic.
 4. The assembly of claim 3 wherein thethermoplastic body has a durometer reading in the range of about 37Shore D to 52 Shore D and a flexural modulus in the range of about30,000 to 70,000 psi.
 5. The assembly of claim 1 wherein the plastic ofthe body is a thermosetting plastic.